The Atacama Cosmology Telescope: the stellar content of galaxy clusters selected using the Sunyaev-Zel’dovich effect

We present a first measurement of the stellar mass component of galaxy clusters selected via the Sunyaev-Zel’dovich (SZ) effect, using 3.6 and 4.5 mu m photometry from the Spitzer Space Telescope. Our sample consists of 14 clusters detected by the Atacama Cosmology Telescope (ACT), which span the redshift range 0.27 < z < 1.07 (median z = 0.50) and have dynamical mass measurements, accurate to about 30 per cent, with median M-500 = 6.9 x 10(14) M-circle dot. We measure the 3.6 and 4.5 mu m galaxy luminosity functions, finding the characteristic magnitude (m*) and faint-end slope (alpha) to be similar to those for infrared-selected cluster samples. We perform the first measurements of the scaling of SZ observables (Y-500 and y(0)) with both brightest cluster galaxy (BCG) stellar mass and total cluster stellar mass (M-500(star)). We find a significant correlation between BCG stellar mass and Y-500 (E(z)(-2/3) D-A(2) Y-500 proportional to M-*(1.2 +/- 0.6)), although we are not able to obtain a strong constraint on the slope of the relation due to the small sample size. Additionally, we obtain E(z)(-2/3) D-A(2) Y-500 proportional to M-500(star) (1.0 +/- 0.6) for the scaling with total stellar mass. The mass fraction in stars spans the range 0.006-0.034, with the second ranked cluster in terms of dynamical mass (ACT-CL J0237-4939) having an unusually low total stellar mass and the lowest stellar mass fraction. For the five clusters with gas mass measurements available in the literature, we see no evidence for a shortfall of baryons relative to the cosmic mean value